Lifting device for lifting and/or lowering an ordered stack of articles

ABSTRACT

A lifting method and device. A first lifting device lifts a multi-layer stack of articles from a lower position upwardly to a raised position at which the uppermost layer is at a desired level for removal of articles. The first lifting device continues to move the stack upwardly in increments for subsequent removal of articles in subsequent layers at the desired level. A second lifting device engages the bottom of the stack at locations different from the areas engaged by the first lifting device for continuing upward movement of the stack for positioning the remaining layers at the desired level for the removal of articles therefrom. The first lifting device is then movable downwardly to receive a new stack and the second lifting means is foldable to a retracted position and movable to a position below the new stack.

FIELD OF THE INVENTION

The invention relates to a lifting device for lifting an ordered stackof articles, which lifting device is intended for cooperating with anunstacking device and with a stack-feeding conveyor.

The device is particularly intended for an unstacking device in whichthe articles to be fed are discharged from above. The stacks that areunstacked in the lifting device, are moved to the lifting device by astack-feeding conveyor

BACKGROUND OF THE INVENTION

A problem involved in known lifting devices intended for cooperatingwith an unstacking device is that the unstacking process is interruptedwhen a complete stach has been unstacked in the lifting device and a newstack is to be fed into the lifting device. In the known devices, duringthe feed of a complete stack to the lifting device, it is not possibleto continue the unstacking process. As a consequence, in the knownlifting devices, the discharge of the articles removed from a stackcannot take place in a continuous manner. Such discontinuous dischargeof articles is generally undesired.

SUMMARY OF THE INVENTION

The object of the invention is to provide a lifting device without theabove-mentioned drawbacks.

To this end, the lifting device is characterized by the features ofclaim 1.

Due to the particular cooperation of the first lifting means and thesecond lifting means, the uppermost article of a stack located in thelifting device can, when the lifting device cooperates with anunstacking device, in each case be removed from the same place in acontinuous manner. In this context, ‘continuous’ must at least beunderstood to mean ‘at a fixed rhythm’. As soon as an article has beenremoved from the stack, the lifting means will move the stack located inthe lifting device slightly upwards, causing a next uppermost article tobe located at the fixed, desired level, whence that next article canthen be removed again by the unstacking device.

As the lifting device possesses first lifting means and second liftingmeans, a completely formed stack and a partially formed stack cansimultaneously be located in the device. As a result, when the liftingdevice cooperates with an unstacking device, a second complete stack canbe fed to the lifting device and received by the first lifting means,while the second lifting means support an already partially unstackedfirst stack, so that an uppermost article of this first stack is alwayskept at the desired fixed level. As soon as the first stack has beenunstacked completely, the uppermost article of the second stack is movedto the desired fixed level, so that the unstacking procedure can becontinued without interruption. In the meantime, the second liftingmeans can, after a passage of time, take over the second stack from thefirst lifting means, after which the first lifting means are moved intoa position in which they are ready to receive a third stack.

Summarizing, it can be stated that the presence of the first liftingmeans and the second lifting means enables a continuous unstackingprocess, which unstacking process need not be interrupted for feeding ordischarging a complete stack of articles. The lifting device accordingto the invention can be realized in a relatively simple manner and canhence be manufactured in an economical manner. As the lifting frames canbe brought from a folded-down position into a folded-up position, thelifting frames can pass an entirely or partially formed stack invertical direction, which is important for causing the unstackingprocess to take place in a continuous manner.

In should be noted that from U.S. Pat. No. 2,205,767 a stacking deviceis known which comprises first and second lifting means. The secondlifting means do engage the lower side of the lowermost article of thestack in the same area as the second lifting means. Consequently, thefirst and second lifting means cannot pass each other. Further, thearticles which are supported by the second lifting means have to beremoved from the second lifting means by retracting the second liftingmeans and thereby shifting the stack over the second lifting means.

From U.S. Pat. No. 2,895,624 a stacking device is known for forming astack of article on a bunk. The known device has first and secondlifting elements which engage the lower side of the bunk. The movementand the relative position of the first and second lifting means iscoupled by a chain. Consequently, the first lifting means cannot takeover a stack from the second lifting means. As a consequence, the supplyof articles to the board on which the articles have to be stacked mustbe interrupted for some time to position an empty bunk while removing abunk containing a full stack. In view thereof the supply of articles tobe stacked cannot be and is not continuous.

Further elaborations of the invention are described in the subclaims andwill be specified on the basis of an exemplary embodiment, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view of an exemplary embodiment of the device in afirst condition;

FIG. 2 is a front view similar to FIG. 1, in a second condition;

FIG. 3 is a front view similar to FIGS. 1 and 2, in a third condition;

FIG. 4 is a top plan view of the device shown in FIGS. 1-3; and

FIG. 5 is a left-side view of the lifting device shown in FIGS. 1-3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lifting device shown in FIGS. 1-5 is intended for lifting an orderedstack S of articles V. In the present case, this concerns trays filledwith eggs. However, it may also concern boxes of eggs or other articlesto be stacked having a substantially rectangular section. The liftingdevice is in particular intended for cooperating with an unstackingdevice and with a stack-feeding conveyor.

The lifting device comprises first lifting means constructed as avertically adjustable lifting table 1 and second lifting meansconstructed as lifting frames 2. These lifting frames can likewise beadjusted upwards and downwards and can moreover assume a folded-down andfolded-up position. The lifting table 1 engages a first area of thelower side of a lowermost article Vb of a stack S. In a folded-downposition, the lifting frames 2 engage a second area of the lower side ofthe lowermost article Vb of the stack S, while the first area and thesecond area do not coincide. In the folded-up position, the liftingframes 2 can pass a stack S in vertical direction. As FIG. 4 clearlydemonstrates, the lifting table 1 and the lifting frames 2 are of aconstruction such that the first area is formed by a central part of thelower side of the lowermost article Vb, while the second area is formedby a part of the lower side of the lowermost article Vb which partsurrounds the central part.

The lifting device according to the present exemplary embodimentcomprises first drive means 3, 4 intended for adjusting the height ofthe lifting table 1 and second drive means 5, 6 intended for adjustingthe height of the lifting frames 2.

The first lifting means comprise a drive cam 3 controlling the positionof the lever 4. The cam 3 is driven by a drive motor 7. The lever 4 hasone end 4 a thereof pivotally and/or slidably connected to a part whichis fixedly connected to the lifting table 1. Rotation of the cam 3causes a pivotal movement of the lever 4, which pivotal movement in turnresults in a height adjustment of the table 1. The second drive means 5,6 likewise comprise a cam 5 determining the position of a pivotallybearing-mounted lever 6. The lever 6 has one end 6 a thereof pivotallyand/or slidably connected to a part which is fixedly connected to thelifting frames 2. The position of the lever 6 and, accordingly, thevertical position of the lifting frames 2 is determined by the rotativeposition of the cam 5, which rotative position is in turn determined bythe drive motor 7. The two cams 3, 5 are mounted so as to be restrainedfrom rotation on a common shaft 10 driven by a chain or belt 11, whichis in turn driven by the motor 7. To provide that a complete stack S iscompletely supported when it is being slid into or out of the liftingdevice, a supporting element 8, 9 is preferably located on either sideof the lifting table 1, at the level of the lowermost position of thislifting table 1. In the present exemplary embodiment, these supportingelements 8, 9 are designed as endless conveyors 8, 9 whose feed ends 8a, 9 a are intended to connect to a stack-feeding and stack-dischargingdevice respectively, such as for instance a conveyor belt. In thepresent exemplary embodiment, the drive of these endless conveyors 8, 9is also connected to the drive motor 7, via chain wheels or pulleys andchains or belts cooperating therewith. It is thus effected that allmovements of the lifting table 1, the lifting frames 2 and the endlessconveyors 8, 9 are intercoupled. It is observed that instead of theendless conveyor belts 8, 9 as supporting elements, plate parts may alsobe used, extending on either side of the lifting table 1 so as toprovide, with the lifting table 1, a supporting surface which fullysupports the entire stack.

When intended for cooperating with the unstacking device, the operationof the lifting device is as follows:

When a first stack of articles is being fed into the lifting device, thelifting table 1 is in a lowermost position. If necessary, the liftingframes 2 can support the last article or the last few articles of apreceding stack and the lifting frames are virtually in the uppermostposition. This position is shown in FIG. 1, in which the lifting table 1is in the lowermost position and the lifting frames 2 are in anuppermost position, in folded-down condition. When the last article Vtof the preceding stack has been removed from the lifting frames 2, thelifting frames 2 are folded up and the lifting table 1 is moved upwardsstepwise, so that in each case the uppermost article Vt can be removedfrom the stack S and it is provided that the uppermost article Vt of thestack S is always at the same fixed level. The meanwhile folded-uplifting frames 2 are moved to a level below the lifting table 1. Thiscondition is shown in FIG. 2. Next, the lifting frames 2 can be foldeddown and moved up again for taking over the support of the stack S. Thiscondition is shown in FIG. 3. In FIG. 3, the stack S is still supportedby the lifting table 1, but the lifting frames 2 are about to take overthe support of the stack S. Next, the lifting table 1 is moved down tothe lowermost position, to be ready for receiving a next stack ofarticles, while the lifting frames 2 move up stepwise. The steppedupward movement of the lifting frames 2, too, takes place such that theuppermost article Vt of the stack S is always at the same fixed level atthe right moment for the desired duration. In this condition, thelifting device is ready to repeat the above-described procedure for anext stack.

It is readily understood that the invention is not limited to theexemplary embodiment described, but that various modifications arepossible within the framework of the invention. For instance, the drivemay also take place by means of two motors which, via a gear wheel and agear rack, engage movable frame parts mounting the lifting frames 2 andthe lifting table 1. Also, the lifting frames 2 and the lifting table 1may have a different shape and the manner of feeding and discharging astack S to and from the lifting device may be varied. One may forinstance think of a pusher plate pushing a stack from or into thelifting device. It is essential that the lifting device be provided withfirst and second lifting means, causing the uppermost article of anuppermost stack located in the lifting device to be always at the samelevel, so that the stacking and/or unstacking process can take place ina continuous manner.

We claim:
 1. A lifting device for lifting an ordered stack of articles,said lifting device cooperating with an unstacking device and with astack-feeding conveyor, the lifting device comprising: first liftingmeans and second lifting means, said first lifting means and secondlifting means cooperating such that the device continuously keeps anuppermost article of a stack located in the lifting device at a fixed,desired level, the first lifting means being constructed as a verticallyadjustable lifting table, the lifting table engaging a first area of alower side of a lowermost article of the stack, the second lifting meansbeing constructed as lifting frames, the lifting frames in a folded-downposition engaging a second area of the lower side of the lowermostarticle of the stack, while the first area and the second area do notcoincide, and the lifting frames in a folded-up position being moveablefrom above a stack around the sides thereof to an operative positionbeneath a subsequent stack, the lifting table and the lifting framesbeing of a construction such that the first area is formed by a centralpart of the lower side of the lowermost article which part surrounds thecentral part, the lifting device comprising first drive means foradjusting height of the lifting table and second drive means foradjusting height of the lifting frames.
 2. A lifting device according toclaim 1 wherein the first and second drive means each comprise a cam androd system, and a common motor driving the cam and rod system.
 3. Alifting device according to claim 1 wherein a supporting element islocated on either side of the lifting table, substantially level to alowermost position of the lifting table, so that during feeding of astack, into the lifting device, said stack is supported oversubstantially the entire lower side of the lowermost article thereof. 4.A lifting device according to claim 1 wherein the two supportingelements located on either side of the lifting table are designed asendless conveyors whose feed ends are connected to said stack-feedingand stack discharging device.
 5. A lifting device according to claim 1wherein said lifting device cooperates with the unstacking device, thedrive of the lifting table and the lifting frames being such that when afirst stack of articles is being fed into the lifting device, thelifting table is in a lowermost position, the lifting table beingsubsequently moveable upwards stepwise until a number of articles havebeen removed from the first stack, the lifting frames, then beingsubsequently foldable down and moveable upwardly for taking over thesupport of the stack of articles, after the lifting table issubsequently moved down to the lowermost position, to be ready toreceive a second stack of articles, while the lifting frames move upstepwise, the stepped upward movement of the lifting table and thelifting frames taking place such that the uppermost article of the stackis always at the same fixed level.
 6. A lifting device for lifting amulti-layered stack of ordered articles from a lower position to araised position whereat the uppermost layer is at a desired level whereit can be removed from the stack, a first lifting means for lifting thestack from said lower position upwardly to said raised position at whichthe uppermost layer can be removed from the stack and for moving thestack farther upwardly to permit at least some of the subsequentremaining uppermost layers to reach said desired level and be removedfrom the stack, a second lifting means for engaging the bottom of thestack at locations on the bottom of the stack different from locationswhere the first lifting means engages the bottom of the stack forfurther raising the stack to bring the remaining layers of the stack tothe desired level where they can be removed from the stack, and saidsecond lifting means being movable between a generally horizontaloperative position at which it can engage and support the bottom of astack and a retracted position wherein it can move from above a stackaround the sides thereof to an operative position beneath a subsequentstack.
 7. The lifting device of claim 6 wherein said first lifting meanscomprises a vertically adjustable lifting table.
 8. The lifting deviceof claim 7 wherein said second lifting means comprise lifting frameswhich can be folded up and down.
 9. The lifting device of claim 8further comprising first drive means for adjusting height of the liftingtable and second drive means for adjusting height of the lifting frames.10. The lifting device of claim 9 wherein said first and second drivemeans comprise a cam and rod system.
 11. The device of claims 10including a common motor for said cam and rod system.
 12. The liftingdevice of claim 6 further comprising supporting elements located oneither side of the first lifting means in order to support substantiallyan entire bottom side of a lowermost layer of articles in the stack. 13.The lifting device of claim 12 wherein said supporting elements areendless conveyors having feed ends connectable to a stack-feeding andstack-discharging device.